The present invention relates to developer compositions for photographic elements comprising photosensitive coatings on substrates, or more particularly to developer compositions for removing the non-image areas of exposed positive working lithographic printing plates.
In the past, various methods of developing printing plates have been employed. One of such methods is to use solvents such as isopropyl alcohol, butyl alcohol, benzyl alcohol, and ethylene glycol monoethyl ether to remove the non-image plate areas. Such solvents are disadvantageous since they are relatively expensive and have a tendency to remove some of the image along with the non-image areas during development.
Others have used caustic inorganic compounds such as trisodium phosphate, sodium hydroxide or sodium metasilicate. However, these can be dangerous to handle and have a high tendency to attack the substrate on which the photosensitive coating is placed. This is particularly true of aluminum which is used for most lithographic printing plates.
U.S. Pat. Nos. 3,891,439 and 4,147,545 employ aqueous solutions of organic lithium salts, such as lithium benzoate as the developer composition. These, however, have the disadvantage of a relatively slow development time, and are taught to work only on negative working printing plates.
The above mentioned developers of the prior art have several disadvantages. When the solution of sodium metasilicate or trisodium phosphate is adjusted to pH about 13 with sodium hydroxide to achieve high development speed, the developer becomes extremely corrosive toward the oxide layer of the aluminum substrate. When the amount of sodium hydroxide is reduced to minimize the corrosive action toward the oxide layer of the aluminum substrate, the speed of development becomes too slow for any practical purpose.
In addition, the reaction product of the caustic with the aluminum substrate such as in the form of aluminum silicate, is substantially insoluble in the developer. These precipitates in the developer solution are disadvantageous for use in a developing machine since they interfere with development and can cause machine damage.